The internal temperature of a constant velocity universal joint changes due to the moving internal components and the influence of the external environment. These temperature fluctuations tend to cause changes in the internal pressure of the joint. However, it is important to keep the internal pressure more or less equal to the outside atmospheric pressure because if the internal pressure changes, the boot, which closes the sealed chamber in which the joint operates, may deform and cause a failure of the seal. In the past, internal pressure equalization has been accomplished by adding one or more vent holes to the outer race or grease cap, or placing a groove in the mating interface between the inner race stub shaft and the boot. The drawback of these attempts at pressure equalization is that the joint can ingest contaminates through the vent holes, often resulting in joint failure.